paulo57509

In the process of repairing small dash panel that is delaminating, I re-installed the remaining lower dash panels in order to be able to drive the vehicle.

Reconnected the battery and the low fuel light was on, even with the gauge showing ~1/4 tank. Drove to the fuel station and filled the tank. Took ~18 gallons which is close to 3/4 tank. The "Range Approx" display read substantially lower than normal; normal hovers around 390 miles.

Tonight, after driving 305.1 miles, this:

Three possibilities, all labor intensive:

1. Gauge is bad.
2. Sender is bad.
3. Gauge cluster is bad.

I can't imagine that anything I did caused any of the three possibilities. Before I tear into this, I'm going to go back and recheck and review my work. I just wish it wasn't +100F outside.

Yamae

I'd check the voltage from the sender gauge. It should be like this below. The gas level is sent from the pin #2 of the connector very close to the tank and to the pin #12 of connector B behind the gauge unit. Sorry that these are from JDM 98 Celsior's drawings but your LS400 should be the same or very similar.





You filled 18 gallons of gas and it should be 3 volt or a bit more. If the voltage is OK, the problem must be caused by the gauge side. I suspect that the problem is caused by the poor connection of the connector or some static discharge. In case of a static discharge issue, a reset may be effective. What I mean by reset is to disconnect the battery for 10 minutes or more and then connect again.

paulo57509

Thank you, Yamae. I was ready to follow the path you provided; confirm the gauge is reading correctly and go from there. However, I will try the reset first.

Thanks again.

clipster

FWIW my 98 started doing the same recently and I haven't touched my instrument cluster. Full tank reads full, half tank reads 3/4, and empty reads just below half. The computer and dummy light are still accurate, so I just leave it at 'X miles since refuel' then at 300 miles I switch to 'Range Approx X'

vidlev

My fuel gauge started acting up awhile ago - I suspected fuel sender so I replaced, to no change.

My trip computer was always accurate but the gauge was totally off. My needle would show full until I’d driven almost 200 miles, then it would slowly come down towards “e”. When I had approx 50 miles to empty the gauge would still show almost 1/3 tank of gas. However as I said the computer was always accurate and my low fuel light would illuminate at seemingly the correct time.

Recently I replaced the gauge itself. This completely fixed my problem and needle is now accurate through the entire range. I never tried to take apart and see if there was something obviously wrong that I could fix.

vidlev

Paolo, based on your cluster pic looks like your LS is 98+? Mine is 98 and new oem gauge is still available from Lexus for approximately $200. Might be able to find cheaper if you really shop around.

pn is 83882-50010

paulo57509

Thanks all for the help. I haven't had the chance to crawl into the trunk to determine if it's the gauge, the sender.

A Corvette owner told me to add Techron to the next fill-up; Techron would sometimes remedy odd gauge behavior. I had forgotten about how wonky GM sending units could get with age. Some theorize that Techron cleans deposit build-up (sulfur) on the variable resistor.

paulo57509

Finally got cool enough outside to crawl around in the trunk to get to the fuel level sensor.

Testing the sender yielded the following results:

Conditions:

• Tank was physically about 3/8 full based on mileage driven.
• Gauge read just under 3/4 full.
• Distance to empty read 168 miles.

Test 1 - Unplug harness from sender; turn key ON.

• Expected Result - Gauge indicates empty.
• Test Result - Gauge didn't move.

Test 2 - Jumper terminals 2 and 3 on harness side, turn key ON.

• Expected Result - Gauge indicates full.
• Test Result - Gauge reads empty (low fuel light and text warning on instrument panel).

I didn't see the need to further diagnose the system. The combination meter will have to be removed and tested/repaired. I had a new, OEM sending unit so it was installed before re-assembling the trunk.